L0301P65 - Haematopoietic Stem Cell Biology
__TOC__ Potency *number of possible fates open to a cell *decreases with age and during differentiation, except for some stem cells (SC) Terms Totipotent *all fates possible **i.e. zygote *can form any cell of the embryo Pluripotent *many cell fates **i.e. embryonic cells *differentiate into cells derived from the three germ cell layers Multipotent *can produce cells of a closely related family of cells Uni/Bipotent *one / two fates are open to them *only produce one cell type, but has the self renewal property which distinguishes them from the non stem cells Properties of Stem Cells Self Renewal *the ability to go through numerous cycles of cell division while maintaining the undifferentiated state Potency *the capacity to differentiate into specialised cell types Major Types of Stem Cells Embryonic Stem Cells *from blastocysts left over from In-Vitro fertilisation in the laboratory *from aborted foetuses = many ethical issues Adult Stem Cells *stem cells have been found in the blood, bone marrow, liver, kidney, cornea, dental pulp, umbilical cord, brain, skin, muscle, salivary gland etc. Comparison Stem Cells *cells of variable potency that can self renew **despite the hype, stem cells are normally used for organ maintenance and repair **the hype about these cells is that there is a question of their therapeutic potential **repair damaged organ by introducing stem cells **does it actually work? Autologous Transplantation *using cells from the patient themselves *e.g. haematopoietic stem cell transplants and skin cell transplants Notion of Commitment *originally thought that differentiated cells were not able to return to their undifferentiated form *however research now has shown otherwise **induced pluripotent stem cells Stem Cells Division *SC divide quite slowly *variable potency during division as cells begin to become somewhat committed *is asymmetrical **results in a stem cell and a progenitor cell (more committed and divide more rapidly) *differentiated cell types - the number of cell types reflects potency of the stem cell *lineage - set of cell types arising from a stem / progenitor cell Discovery *came about by people trying to ascertain how long cells live *turnover assay (t1/2) – cells do not live forever ∴they must be replaced (by SCs) *detected via pulse/chase assay *all organs show cell turnover at different rates **e.g.: RBCs t1/2 120 days; small intestine t1/2 3-5 days; hair t1/2 4 years Pulse / Chase Analysis Pulse *add radio-labelled nucleotide, BrdU (bromodeoxyuridine) for short time so that it is incorporated into DNA Chase *add lots of unlabelled thymidine which follow cells over long time Half Life *determined when BrdU has diminished by a half *assay half life of labelled population also can label lineage  Isolation and Assay *adult SCs are very rare and hard to isolate **haematopoietic stem cells comprise ~0.01% of bone marrow cells *isolation via fluorescent activated cell sorting (FACS) **label stem cells via cell surface proteins with “tagged” antibodies ***sort individual cells ***assay for stem cell properties   Assays for Stem Cell Function *repopulation assay or transplant assay **transplanting test stem cells in the adult **remove the adult endogenous cells that may be competing *in-vitro induction **cells and inducers *embryo incorporation **test in chimeric embryo  Regulation of Stem Cells *can be kept quiescent (inactive) **by signals from surrounding cells “niche” **in some types of activation by environmental input, the niche cells induce the stem cells to divide ***stem cell and progenitor ***niche cells do this by changing their signalling Stem Cell Niche *refers to the environment around the cell *composed of microenvironmental cells that: **nurture stem cells **protect from apoptosis, excessive differentiation (loss of reserve) **prevent excessive proliferation (cancer risk) *e.g.: mesenchymal cells, nerve cells & osteoblasts are main haemopoietic ‘niche’ cells Therapeutics *the dream is that you have a stem cell population for all your cells in the body; so you can inject the appropriate stem cells to regenerate cell of interest *idea - inject stem cells to repair damaged organs *problem - need stem cells with correct potency **adult stem cells are very rare **are there any appropriate substitutes?  Embryonic Stem Cells *derived from inner cells mass of an early mammalian embryo *grow out embryonic SC lines - continuous growth in culture *each has unique potency and can be used to do different things Cord Blood Stem Cells *blood is collected from umbilical cord immediately after delivery *about 100- 150cc (cm3) *number of cells in 1 ml is 40,000 *stored in blood banks at -19℃ in a state of suspended animation and restart their activity on thawing Issues with Embryonic Stem Cells *Ethical - harvest and obtain human embryos **currently not allowed! **trying to play God? **is embryo a person? **will stem cell research encourage embryo destruction and abortions? *these cells are non-autologous **do not match the immune system of the recipient therefore may get rejected  Induced Pluripotent Stem (IPS) Cells *convert adult cells into stem cells by insertion of only 4 genes *advantage **self *disadvantage **not proven and still lots of problems for research Mechanisms of Reprogramming *transcription factor activation *signalling pathways *epigenetic regulation Source of Stem Cells *human embryonic stem cells (banned) *bone marrow derived *derived from other organs *iPS (in the future) Clinical Application *administer stem cells directly in vivo, they will ‘home’ to the appropriate tissues *inject stem cells directly into the organ of interest *differentiate stem cells ex vivo into the desired lineage and then administer   Bone Marrow Transplantation *peripheral blood stem cell transplantation *for leukemias, lymphomas, aplastic anaemias *solid tumours etc   Transplantation Therapy *for acute and chronic degenerative disease Examples *epidermal **skin graft for patients with severe burns *neuronal **Parkinson’s disease **multiple sclerosis **other neurodegenerative diseases *liver **for liver damage by drugs, toxins or viral infection *islet cells in pancreas **for insulin non-producing pancreas *skeletal muscle satellite **muscular dystrophies or muscle loss *mesenchymal **tissue engineering in plastic reconstructive surgery *gene therapy Importance of Stem Cell Research *stem cells allow us to study how organisms grow and develop over time *stem cells can replace diseased or damaged cells that can not heal or renew themselves *we can test different substances (drugs and chemicals) on stem cells *we can get a better understanding of our “genetic machinery”